Substantial Improvement

When buildings undergo repair or improvement, it is an opportunity for floodplain management programs to reduce flood damage to existing structures. More than 21,000 communities participate in the National Flood Insurance Program (NFIP) by adopting and enforcing regulations and codes that apply to development in Special Flood Hazard Areas (SFHAs). Rock Island County's floodplain management regulations and codes meet the minimum NFIP requirements that are not only for new structures, but also for existing structures that are not compliant with our regulations. 

In order for Rock Island County residents to be able to participate in the NFIP, one of the duties we must perform, is to determine whether proposed work qualifies as a substantial improvement or repair of substantial damage (referred to as an “SI/SD determination”). If work on buildings constitutes SI/SD, then structures must be brought into compliance with our requirements for new construction, including the requirement that lowest floors be elevated two feet above the base flood elevation (BFE). The our ordinance defines SI/SD as follows: 

  • SUBSTANTIAL DAMAGE. Damage of any origin sustained by a structure whereby the cumulative percentage of damage during a ten-year period ending on the date of the last damage event equals or exceeds 50% of the market value of the structure before the damage occurred regardless of actual repair work performed. The term includes Repetitive Loss Structures.
  • SUBSTANTIAL IMPROVEMENT. Any reconstruction, rehabilitation, addition, or improvement of a structure taking place during the life of the structure in which the cumulative percentage of improvements equals or exceeds 50% of the market value of the structure before the improvement or repair is started, or increases the floor area by more than 20%. Substantial Improvement is considered to occur when the first alteration of any wall, ceiling, floor, or other structural part of the building commences, whether or not that alteration affects the external dimensions of the structure. This term includes structures which have incurred repetitive loss or substantial damage, regardless of the actual repair work done.

Procedures for documenting SI/SD.

  • Staff will determine the market value or require the applicant to obtain an appraisal of the market value prepared by a qualified independent appraiser of the building before the start of construction of the proposed work. In the case of repair, the market value of the building shall be the market value before the damage occurred and before any repairs are made. (This is only the structure's value, not the land.) 
  • Staff will compare the cost to perform the improvement, the cost to repair a damaged building to its pre-damaged condition, or the combined costs of improvements and repairs, if applicable, to the market value of the building.
  • Staff will determine and document whether the proposed work constitutes substantial improvement or substantial damage.
  • Staff will notify the applicant if it is determined that the work constitutes substantial improvement or repair of substantial damage and that compliance with the flood resistant construction requirements of this subchapter.
  • A form shall be used to document the actual calculations for projects and may be required to be recorded in the County Recorder office if the improvements exceed 20%.